js实现日期的相加减

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
 <head>
  <title> New Document </title>
  <meta name="Generator" content="EditPlus">
  <meta name="Author" content="">
  <meta name="Keywords" content="">
  <meta name="Description" content="">

  <script type="text/javascript">

function dateOperator(date,days,operator)

{

    date = date.replace(/-/g,"/"); //更改日期格式
	var nd = new Date(date);
	nd = nd.valueOf();
	if(operator=="+"){
	 nd = nd + days * 24 * 60 * 60 * 1000;
	}else if(operator=="-"){
		nd = nd - days * 24 * 60 * 60 * 1000;
	}else{
		return false;
	}
	nd = new Date(nd);

	var y = nd.getFullYear();
	var m = nd.getMonth()+1;
	var d = nd.getDate();
	if(m <= 9) m = "0"+m;
	if(d <= 9) d = "0"+d;
	var cdate = y+"-"+m+"-"+d;
	return cdate;
}

//相减
alert(dateOperator("2014-01-01",1,"-")) ;
//相加
alert(dateOperator("2014-01-01",1,"+")) ;

</script> 

  </script>
 </head>

 <body>

 </body>
</html>